(1) Field of the Invention
The present invention relates to thin sheet composite compositions with improved barrier properties particularly in reference to oxygen and hydrogen. In particular, the present invention relates to compositions including a fabric layer with a polymer impregnated into the fabric layer to provide sheets. In particular, the sheet composites have a permeability to oxygen in the direction perpendicular to the sheet that is less than one-tenth the transmission rate for the fabric layer alone and less than one-fifth the transmission rate for the polymer alone without the fabric layer.
(2) Description of Related Art
The prior art has described various polymer and particle and/or fiber composites which have a limited transmission rate to gases, particularly oxygen, and water. The problem is that the oxygen transmission rate of these prior art composites is either significantly greater than 100 cc.mil/m2.day.atm (6.45 cc.mil/100 in/day) or less than five times smaller than the permeability of the pristine polymer alone. Furthermore the prior art particle composites have to be coated as a liquid suspension onto a polymer substrate through dip coating or spraying processes and dried or cured as in PCT/US00/03802. These coating methodologies inevitably lead to less than optimal particle orientations which compromise the barrier properties toward small molecules. Theoretical modeling studies by Nagy and Duxbury in Physical Review E66, 2002, 020802(R) have shown that for typical polymer composites reinforced by dispersed clay nanolayers with a width to thickness aspect ratio of 128, even small mis-alignments of the platelets causes the permeability to be dramatically reduced and far lower than the barrier properties expected on the basis of well-aligned particles. Thus, there is a need for improved thin sheet composite compositions in which the alignment of nanoparticles is substantially improved and for which the gas permeability transmission rates are reduced to values near those expected for well aligned particles.
PCT Publication No. WO 00/40404 to Chu et al describes a barrier composite compositions which comprises nano-scale particles with permeabilities that are several times lower than the permeabilities of the pristine polymer. In this case the nano particles are mixed with a liquid polymer and the fluid mixture is coated onto a substrate surface to obtain a barrier film. The amounts of nanoparticles used are relatively low so that the particles constitute 5 to 20 weight percent and which maintain the clarity often desired for certain applications. Higher loadings of nanoparticles compromise the fluidity of the suspension, making it difficult to apply the suspension to the surface to achieve a uniform coating. Thus, to achieve thicker coatings with better barriers, one must repeat the dip coating or spray coating process several times. U.S. Pat. No. 6,337,046 B1 is similar in content to the Chu et al application.
Various coatings are used on plastic surfaces as a barrier to limit transmission of oxygen and water. These coatings are generally for the purpose of maintaining the clarity of a clear substrate. Illustrative is U.S. Patent Publication No. 2002/0006518 A1 where clay is used as the coating. Particles of silica and metals have also been used as barrier coatings. Particle coatings are often discontinuous or irregular, lack abrasion resistance, and do not adhere well to the polymer surfaces to which they are applied.